1 //===-- WebAssemblyCallIndirectFixup.cpp - Fix call_indirects -------------===//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 ///
10 /// \file
11 /// \brief This file converts pseudo call_indirect instructions into real
12 /// call_indirects.
13 ///
14 /// The order of arguments for a call_indirect is the arguments to the function
15 /// call, followed by the function pointer. There's no natural way to express
16 /// a machineinstr with varargs followed by one more arg, so we express it as
17 /// the function pointer followed by varargs, then rewrite it here.
18 ///
19 /// We need to rewrite the order of the arguments on the machineinstrs
20 /// themselves so that register stackification knows the order they'll be
21 /// executed in.
22 ///
23 //===----------------------------------------------------------------------===//
24 
25 #include "WebAssembly.h"
26 #include "MCTargetDesc/WebAssemblyMCTargetDesc.h" // for WebAssembly::ARGUMENT_*
27 #include "WebAssemblyMachineFunctionInfo.h"
28 #include "WebAssemblySubtarget.h"
29 #include "llvm/Analysis/AliasAnalysis.h"
30 #include "llvm/CodeGen/LiveIntervalAnalysis.h"
31 #include "llvm/CodeGen/MachineBlockFrequencyInfo.h"
32 #include "llvm/CodeGen/MachineDominators.h"
33 #include "llvm/CodeGen/MachineInstrBuilder.h"
34 #include "llvm/CodeGen/MachineRegisterInfo.h"
35 #include "llvm/CodeGen/Passes.h"
36 #include "llvm/Support/Debug.h"
37 #include "llvm/Support/raw_ostream.h"
38 using namespace llvm;
39 
40 #define DEBUG_TYPE "wasm-call-indirect-fixup"
41 
42 namespace {
43 class WebAssemblyCallIndirectFixup final : public MachineFunctionPass {
44   StringRef getPassName() const override {
45     return "WebAssembly CallIndirect Fixup";
46   }
47 
48   bool runOnMachineFunction(MachineFunction &MF) override;
49 
50 public:
51   static char ID; // Pass identification, replacement for typeid
52   WebAssemblyCallIndirectFixup() : MachineFunctionPass(ID) {}
53 };
54 } // end anonymous namespace
55 
56 char WebAssemblyCallIndirectFixup::ID = 0;
57 FunctionPass *llvm::createWebAssemblyCallIndirectFixup() {
58   return new WebAssemblyCallIndirectFixup();
59 }
60 
61 static unsigned GetNonPseudoCallIndirectOpcode(const MachineInstr &MI) {
62   switch (MI.getOpcode()) {
63     using namespace WebAssembly;
64   case PCALL_INDIRECT_VOID: return CALL_INDIRECT_VOID;
65   case PCALL_INDIRECT_I32: return CALL_INDIRECT_I32;
66   case PCALL_INDIRECT_I64: return CALL_INDIRECT_I64;
67   case PCALL_INDIRECT_F32: return CALL_INDIRECT_F32;
68   case PCALL_INDIRECT_F64: return CALL_INDIRECT_F64;
69   case PCALL_INDIRECT_v16i8: return CALL_INDIRECT_v16i8;
70   case PCALL_INDIRECT_v8i16: return CALL_INDIRECT_v8i16;
71   case PCALL_INDIRECT_v4i32: return CALL_INDIRECT_v4i32;
72   case PCALL_INDIRECT_v4f32: return CALL_INDIRECT_v4f32;
73   default: return INSTRUCTION_LIST_END;
74   }
75 }
76 
77 static bool IsPseudoCallIndirect(const MachineInstr &MI) {
78   return GetNonPseudoCallIndirectOpcode(MI) !=
79          WebAssembly::INSTRUCTION_LIST_END;
80 }
81 
82 bool WebAssemblyCallIndirectFixup::runOnMachineFunction(MachineFunction &MF) {
83   DEBUG(dbgs() << "********** Fixing up CALL_INDIRECTs **********\n"
84                << MF.getName() << '\n');
85 
86   bool Changed = false;
87   const WebAssemblyInstrInfo *TII =
88       MF.getSubtarget<WebAssemblySubtarget>().getInstrInfo();
89 
90   for (MachineBasicBlock &MBB : MF) {
91     for (MachineInstr &MI : MBB) {
92       if (IsPseudoCallIndirect(MI)) {
93         DEBUG(dbgs() << "Found call_indirect: " << MI << '\n');
94 
95         // Rewrite pseudo to non-pseudo
96         const MCInstrDesc &Desc = TII->get(GetNonPseudoCallIndirectOpcode(MI));
97         MI.setDesc(Desc);
98 
99         // Rewrite argument order
100         auto Uses = MI.explicit_uses();
101         MachineInstr::mop_iterator it = Uses.begin();
102         const MachineOperand MO = *it;
103 
104         // Set up the flags immediate, which currently has no defined flags
105         // so it's always zero.
106         it->ChangeToImmediate(0);
107 
108         MI.addOperand(MF, MO);
109 
110         DEBUG(dbgs() << "  After transform: " << MI);
111         Changed = true;
112       }
113     }
114   }
115 
116   DEBUG(dbgs() << "\nDone fixing up CALL_INDIRECTs\n\n");
117 
118   return Changed;
119 }
120 
121